function largestOfFour( arr ) {
  const lengthlist = [];
  for ( let i = 0; i < arr.length; i++ ) {
    lengthlist.push( Math.max( ...arr[ i ] ) );
  }
  return lengthlist;
}

console.log( largestOfFour( [
  [ 4, 5, 1, 3 ],
  [ 13, 27, 18, 26 ],
  [ 32, 35, 37, 39 ],
  [ 10, 10, 7, 1 ]
] ) );
